Conversion of PET bottles into carbonaceous adsorbents for Pb(II) removal from aqueous solutions via KOH activation

In this study, we present a novel approach to repurpose waste Polyethylene terephthalate (PET), a prominent contributor to global plastic usage, for the synthesis of efficient adsorbents via facial pyrolysis. The assynthesized adsorbents were applied for the removal of lead (Pb(II)) ions in aqueous solution. Controlled batch experiments at pH 5 with 0.075 g of adsorbent at room temperature (20( degrees)C) were conducted to measure Pb (II) adsorption capacities (mg/g) and fitted on isotherm models (Langmuir, Freundlich, and Temkin) and kinetics models (Pseudo-First order, Pseudo-Second order, and Elovich). Thermodynamic experiments conducted at four different temperatures (293 K, 303 K, 313 K, and 323 K) provided enthalpy, entropy, and Gibbs free energy change parameters, explaining the Pb(II) adsorption behaviors on PET-based adsorbents. The activation process involving KOH, followed by carbonization, yielded adsorbents with exceptional surface areas, pore volumes, and elevated oxygen contents (up to 22.8 %). The best adsorbent exhibited superior performance, achieving a maximum adsorption capacity of 219.7 mg/g within a rapid equilibrium time of 15 min. The adsorption behavior adhered well to the Langmuir isotherm model (R-2 = 0.999) and Pseudo-Second Order kinetics model (R-2 = 0.999). Furthermore, C600K600 displayed outstanding reusability, with negligible efficiency reduction (<5 %) even after five consecutive cycles. These results underscore the successful conversion of PET waste into a lowcost and highly effective adsorbent, offering a promising solution for sustainable waste management.